Apple, Google, other tech giants and a number of noted cryptologists have signed a letter to the Obama administration urging the US government to preserve strong encryption against pressure from law enforcement and surveillance agencies.

The letter argues that “strong encryption is the cornerstone of the modern information economy’s security,” and that the government should “fully support and not undermine efforts to create encryption standards [nor] in any way subvert, undermine, weaken or make vulnerable” commercial software.

Richard A Clarke, one of the review group signatories, made a comparison to a failed attempt to institute back doors in the phone network in the 90s. “If they couldn’t pull it off at the end of the cold war, they sure as hell aren’t going to pull it off now,” he told the newspaper.

With the launch of iOS 8, “the information stored on many iPhones and other Apple devices will be encrypted by default”, Comey told the Brookings Institute in Washington DC last year. “Shortly after Apple’s announcement, Google announced plans to follow suit with its Android operating system. This means the companies themselves won’t be able to unlock phones, laptops and tablets to reveal photos, documents, email and recordings stored within.”

Encryption won't work if it has a back door only the 'good guys' have keys to

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Comey said: “At the outset, Apple says something that is reasonable – that it’s not that big a deal … Apple argues, for example, that its users can back up and store much of their data in ‘the cloud’ and that the FBI can still access that data with lawful authority. But uploading to the cloud doesn’t include all of the stored data on a bad guy’s phone, which has the potential to create a black hole for law enforcement.”

In response to such fears, many, including the British prime minister, David Cameron, have suggested that firms could build back doors in to their encryption – special weaknesses which allow law enforcement and surveillance agencies to break into otherwise secure connections. But the security industry is adamant that such back doors are technologically infeasible.